The present invention relates to a method for feeding a fuel cell with fluid products such as reactants, or liquid electrolyte, and to a device for carrying out this method.
A fuel cell comprises chambers fed with the fluid products necessary to its operation, which are supplied by feeding circuits.
For a better understanding of the following description reference will be made, by way of example only, to a fuel cell comprising:
chambers supplied with a gaseous fuel such as hydrogen, PA1 chambers supplied with a combustion sustaining gas or oxidizer, such as air, and PA1 chambers fed with a liquid electrolyte such as an aqueous solution of potassium hydroxide.
Mainly two methods are used for feeding with the same fluid a plurality of fuel cell chambers.
According to the first of these methods, all the fuel cell chambers are connected in series. Since the fluid reactants are not very pure, it can be ascertained that the impurity content increases from the first to the last chamber traversed by these fluids. Consequently the electrodes which limit these chambers are not under the same operating conditions. This disadvantage can be limited by feeding the chamber with a fluid at a flow rate whose value greatly exceeds that corresponding to the fluid consumption of the fuel cell. This feeding at a high flow rate may either be continuous or intermittent, as in the embodiment shown in FIG. 1 of French Patent No. 1,486,405. In any case this method requires in the feeding circuit of the fuel cell the provision of means for supplying, at least periodically, fluid at high flow rate under a pressure sufficient to compensate for the pressure drops in each fuel cell chamber. Such means has a high power consumption and thus decreases the overall efficiency of the fuel cell.
According to the second method which may be illustrated by FIG. 2 of the above-indicated French Patent all the chambers are connected in parallel to obtain a theoretical pressure drop of reduced value.
Unfortunately, it is difficult with such an arrangement to balance the fluid flow rates in the different chambers. It has been experimentally ascertained that since the fluid flow rates are not the same in the different chambers the impurity content varies from one chamber to another and thus the electrodes limiting these adjacent chambers do not operate under the same conditions. This drawback can be limited by using a fluid distributor located between the feeding circuit and the different chambers. This distributor is for example constituted by capillary conduits connected in series with the chambers or may be designed as illustrated in U.S. Pat. No. 3,589,941. To compensate for the pressure drops through these capillary conduits, it is necessary to use feeding means capable to deliver a pressurized fluid at a high flow rate. The power required to actuate such feeding means substantially reduces the output of the fuel cell.
According to other proposed solutions combining the two above-indicated methods, and illustrated by FIG. 3 of French Pat. No. 1,486,405, the chambers fed with the same fluid are distributed into groups which are interconnected either in series or in parallel, the chambers of each group also being interconnected either in parallel or in series. These solutions also require a high power consumption to circulate the fluid flow through the feeding circuit.
In any event the fluid flow rate through the feeding circuit must be substantially greater than the fluid consumption rate of the fuel cell, so as to limit the concentration of impurities in the chambers.
It has become possible to maintain the impurity content in the fuel cell substantially at a constant value, irrespective of the fluid flow rate feeding the fuel cell, with an average fluid flow rate through the feeding circuit which is about twice the consumption rate of the fuel cell. This has been achieved by designing a feeding circuit comprising a pipe forming a loop which interconnects the inlet and outlet orifices of the fuel cell, fresh fluid being continuously admitted into this loop and a certain fraction of the fluid flowing through the loop being permanently or periodically discharged therefrom.
Nevertheless the power consumed for the fluid circulation reduces the net output of the fuel cell.
Moreover a precise observation of a fluid flow through a fuel cell chamber of given geometry shows that the impurity content is highly variable from a given location of this chamber to another and may sometimes reach such a value that considerable portions of the electrode no longer take part in the production of electric power. This phenomenon is obviously dependent on the shape and size of the chambers and on the relative location of the inlet and outlet orifices for the fluid reactant in these chambers.
It is also known from U.S. Pat. No. 3,268,364 to increase the flow rate of fluid feeding the fuel cell and from U.S. Pat. No. 1,359,881 to use an auxiliary fluid to sweep away water gathered in some of the fuel cell chambers. Such method requires a substantial power consumption for circulating these fluids.